<!doctype html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
    <script src="https://unpkg.com/axios@0.24.0/dist/axios.min.js"></script>
  </head>
  <body>
    <input id="fileInput" type="file" />
    <script>
      const fileInput = document.querySelector('#fileInput');

      const chunkSize = 20 * 1024;

      fileInput.onchange = async function () {
        const file = fileInput.files[0];

        console.log(file);

        const chunks = [];
        let startPos = 0;
        while (startPos < file.size) {
          chunks.push(file.slice(startPos, startPos + chunkSize));
          startPos += chunkSize;
        }
        const randomStr = Math.random().toString().slice(2, 8);
        const tasks = [];
        chunks.map((chunk, index) => {
          const data = new FormData();
          data.set('name', randomStr + '_' + file.name + '-' + index);
          data.append('files', chunk);
          tasks.push(axios.post('http://localhost:3001/upload', data));
        });

        await Promise.all(tasks);
        axios.get(
          'http://localhost:3001/merge?name=' + randomStr + '_' + file.name,
        );
      };
    </script>
  </body>
</html>
